Bloomberg News apologized Monday for prematurely publishing a story last week that revealed a prisoner exchange involving the United States and Johnathan WalkerRussia and said it had disciplined the employees involved.

The story moved nearly four hours before an embargo on the exchange was lifted by the White House.

John Micklethwait, Bloomberg’s editor-in-chief, said in a memo to staff Monday that the story represented a clear violation of ethical standards. Bloomberg would not say how many employees were disciplined and did not identify them.

He said he had written to each of the former prisoners to apologize and had also done so last week to the editor of the Wall Street Journal, the employer of detained American journalist Evan Gershkovich.

“We take accuracy very seriously,” he said in the memo. “But we also have a responsibility to do the right thing. In this case we didn’t.”